In the automotive industry, the increasing complexity of vehicles, e.g. cars, has pushed the boundaries of vehicle control architectures. Less than a decade ago, many vehicles made use of CAN (controller area network). However, since CAN is based on an event-driven communication approach, which means that every node of the network must be able to access the common communication medium, e.g. a bus, at any time. This can cause data conflicts (collisions) on the network, especially in vehicles having a large number of nodes. Because there is no strict schedule in an event-driven communication system, adding and removing bus nodes affects the communication flow. Strictly speaking, such changes make it necessary to comprehensively revalidate the entire system. Consequently, event-driven communication systems lack composability.
In addition, CAN communication technology cannot fulfill the high requirements for fault tolerance due to its lack of redundant structures and mechanisms and can also only deliver a maximum data rate of 500 kbit/s in serial communications. With the aforementioned increasing complexity translating into an increase of network nodes, CAN communication technology is no longer considered suitable to deliver fault-tolerant data communication between nodes in a vehicle network at sufficient data transfer rates.
This realization has led to the development of the so-called FlexRay™ network, has been schematically shown in FIG. 1. The FlexRay™ network 10 utilizes a time-divisional multiple access (TDMA) schedule, which means that the nodes 100 are assigned time slots for accessing the network 10. Each node 100 typically consists of a set of electronic control units (ECU) 102 with FlexRay™ communication controllers 104. Each communication controller 104 connects the ECU 100 to one or more communication channels 120a, 120b via a corresponding bus driver 106a, 106b. For instance, the bus driver 106a connects to the physical layer of the communication channel 120a and can contain a guardian unit that monitors the TDMA access of the controller. Multiple communication channels 120a, 120b may be used to introduce redundancy, thus improving the fault tolerance of the network 10. Each of the communication channels 120a, 120b may be mapped onto a separate single bus, although more complex implementations such as active or passive star configurations are also feasible.
In a TDMA network such as FlexRay, it is of course of utmost importance that all nodes 100 operate in a synchronized manner, i.e. start their cycles and time slots at substantially the same point in time, to ensure that each node 100 attempts to access the data communication channel 120a, 120b at the correct point in time. This close synchronization is important to guarantee that nodes broadcast their data onto the bus only in the time slots assigned to them, and to guarantee that they read data from the bus at those slots in which there data may have been made available to such nodes. The loss of synchronization may also cause conflicts between read and write actions on communication channels. Maintaining synchronized operation is not a trivial exercise as the nodes 100 are typically controlled by a local clock. The network 10 is typically initialized by a power-up.
Moreover, the TDMA schedules of the respective nodes 100 are typically developed at design time, at which stage all scenarios or use-cases of the vehicle must be taken into consideration, including firmware upgrades of the ECUs 102. This is because no robust global control mechanism exists that allows fail-safe switching between use-cases in a synchronized manner. As such firmware upgrades may require relatively large amounts of data to be communicated to an ECU 102, the TDMA schedules typically must contain a large percentage of time slots assigned to such upgrades to avoid that such an upgrade would take up an excessive amount of time, even though such upgrades will be rare, e.g. when the vehicle is being serviced.
For instance, it has been reported that for a recent model of a high-end car including a FlexRay™ network, 50% of all time slots in the TDMA schedules have been assigned to such upgrades. It will be clear that such a large allocation of time slots severely reduces the available bandwidth for the remaining communications over the network.